Variable-speed induction motor



Aug. 10 1926. 1,595,550

D. e. HOWMARD VARIABLE SPEED INDUCTION MOTOR Filed Feb. 10. 1923 g s s t1 A TTORNE V v Aug. 10 .1926. 1,595,550

D. G. HOWARD VARIABLE SPEED INDUCTION MOTOR Filed Feb. 10 1923 2Sheets-Sheet 2 Z7 IIVVENTOR Qwid fiQowmov Patented Aug. 10, 1926. V

UNITED STATES v 1,595,550 PATENT OFFICE.

DAVID G. HOWARD, OF ANNAPOLIS,.MARYLAND.

VARIABLE-SPEED INDUCTION MOTOR.

Application filed February 10, 1923. Serial No. 618,216.

Some of the more important objects of the present invention are toenable the effective operation of an induction motor throughout avconstantly and gradually variable range of speed and to accomplishthis'with a simple, rugged and commercially practicable construction.

Other objects of the invention are to provide a variable speed motorhaving the desired characteristics mentioned, which will be readilysusceptible of either arbitrary or automatic control.

One of the novel features of the invention enabling the attainment ofthe desired results is the mounting of the stator or primary windings atthe opposite sides of or about the axisof the armature 1n such a waythat they may be shifted toward and away from each other substantiallyradially of the armature so as to vary the point of imposition of thetraveling magnetic field radially of the armature and hence applytheforce to the armature at different angular speeds.

Other novel features of the invention relate to the particular methodsof interconnecting the stator windings grouped about the armature forthe purpose of effecting their coooperative adjustment.

In the accompanying drawings forming.

part of this specification I have illustrated but a few examples of thedifferent forms the invention may take and therefore Wish it understoodthat the structure may be modified in various respects without departingfrom the true spirit and scope of the invention as hereinafter definedand claimed.

In the drawings referred to, Figure 1 is a view in side elevation of oneform of the motor.

Figure 2 is a top lan view of the same.

Figure 3 is an en arged detail illustrating diagrammatically the pathsfor the mag: netic flux.

Figure 4 is a side elevation illustrating another method of adjustablymounting the stator windings.

Fig. 4 illustrates a modification of the adjusting mechanism of Fig. 4.

Figures 5 and 6 are side and edge views respectively of another possibleembodiment of the invention.

In the several forms of the invention herein illustrated, the armatureis shown as of disc form, as indicated at 10, but this isby way ofillustration as the rotor or secondary element may be of any usual orspecial design. The disc type of rotor, however, ofi'ers certainadvantages in the matters of simplicity, relatively light weight andrange of possible speed variat1ons and may be constructedwith or withoutconductors embedded therein, as found most advantageous.

The disc form'of rotor offers the further advantage that a number ofsuch'rotors may be mounted tandem on the same shaft 11, spaced just farenough apart for the exciting windings therebetween, thus providing amaximum of power within a fairly compact machine.

The stator or primary windings are preferably constructed after themanner of electromagnets with plane polar surfaces to enable'theeffective and ready adjustment of the same toward and away from thearmature. These stator windings are designated 12 and may in themselvesbe of any usual or special form of distributed or salient pole windingssuch as are provided for polyphase induction motors,v transformers andthe like. Thus in Figure 3 I have illustrated how with a multiplearmature construction the exciting coils may be laid in slots in thefaces of the magnet structures of the stator units divided and arrangedto produce ten polar projections 13 on the end magnets.

At any instant ad'acent pairs of these polar projections will aveopposite polarit' but the polar projections of each pair will have likepolarity. As illustrated in Fig. 3, each pair of polar projections onthe end magnets will correspond to a single polar projection 14 on theinner magnet structures which are disposed between the discs, and willbe placed and connected in a manner to produce a progressive magneticflux cutting the rotor elements in the direction required to produce aturning movement on the armature. These inside magnets are shown ashaving five polar projections of alternate polarity and are connectedand placed as shown to supplement the turning movement produced by theother stator magnets. In all cases the magnetic flux produced by thestator parts cuts the rotor discs in the progressive manner necessaryfor producing rotational torque of the roto discs about their axis.

Various means may be provided for supporting and adjusting the statorwindings ut such means are preferably of such a nature as to efi'ect acontinuously variable adjustment asdistinguished from a step-bystepadjustment so as to provide infinite variations in the speed.

In Figures 1, '2 and 3 I have indicated one simple form of supportingand adjusting means comprising for each rotor a pair of posts 16 havingscrewthreaded portions 17 engaged in screw seats or bosses 18 on thestator elements, thescrewthreads being arranged to operate in theturning of the posts to approach and separate the stator windings andthe posts being connected to turn in unison as by means of suitablegearing 19.

The adjusting screws may be turned by hand, as by means of a handle 20or power actuating means may be provided therefor such as a smallelectric motor indicated at 21 as having a pinion 22 in mesh with thegearing which connects the screws. Electromagnetic or solenoid actionmight also be used for efiecting the shifting, or pneumatic or otherdevices may be employed for the purpose as shown in Fig. 4

The stator windings are grouped about the armature and connected with apolyphase circuit in such a way as to produce the efi"ect of aprogressive magnetic field traveling in the plane of the armature and Iproducing resultant rotation of the armature. By shifting the statorwindings toward and away from each other it will be seen that the radiusof this progressive magnetic field will.be reduced and increased and theforce will thereby be applied to the armature at different distancesfrom the center thereof and hence with lesser or greater leverage and atgreater or less angular speeds. Thus by approaching and separating thestator elements both the speed and the torque of the armature arecontrolled and this through a relatively wide range. Also, the changesare effected gradually so that very fine adjustments can be made.

Where a multiple rotor construction is provided, the shifting means forthe stators of the several rotors will preferably be interconnected asby gearing 30 so that the changing effects on all the rotors will bealike. In Figure 4 I have illustrated another method of mounting thestator windings at opposite sides of the armature axis includingswinging arms 23 supporting the stator elements and pivoted at 24 withgear sectors 25 connecting them so that the arms will swing in unisontoward and away from each other.

In Fig. 4 40 design-ates an actuator connected by a link 41 with a lever42 aflixed tothe shaft 24. This actuator may be a solenoid and core or acylinder and piston and may be either double or single acting. If singleacting, a spring 43 may be provided to oppose its pull.

The stator elements may be placed at such an angle to the radius of'thedisc that there occurs a radial thrust which may be utilized forautomatic control. Furthermore, when placed normal to the radialelements of the disc, the stator is found to be acted upon by anappreciable outward thrust because of its tangential construction andmounting. The weight of the movable elements may be counterbalanced bysuitable springs or weights as indicated at 26 in Figure 4, and thecounterbalancing may be designed to cooperate with the outward thrust ofthe stator elements in effecting an automatic control of the machine,where such an automatic control is desirable, as in cases where constanttorque or constant speed is required. This automatic control of speedand torque is possible as the outward thrust produced on the statorelements is proportional to the turning movement and, therefore, willvary with the load. As stated above, the outward thrust may be madepositive or negative by changing the angle at which the stator elementsare set.

By completely reversing the stator windings it will be seen that areversal of the rotation may be effected. I have illustrated such a.possibility as this in Figures 5 and 6 where the stator elements aremounted on shafts 27 connected together by sprocket chain or othergearing 28 and operable by means of a handle 29 to simultaneously turnthe windings to face the progressive magnetic field from one directioninto a completely opposite direction. In efi'ecting this reversal itwill be clear that as the stator elements are tilted or turnedthroughout the first half revolution the armature will be graduallyslowed down and brought to a stop and will then in a continuation of theturning movement, be started in the reverse direction.

The reluctance of the magnetic circuit may be decreased if founddesirable by the insertion of sections of magnetic material in thenon-magnetic disc 10, which sections may be in the form of plugs 35 asindicated in Figure 1.

The invention, it will be seen, provides a polyphase induction motorhaving the rugged characteristics of the common squirrel cage type andfor any given speed setting having operating characteristics verysimilar, but adapted in addition for infinite speed regulation withinthe limits of construction. Both rotor and stator are of comparativelsimple construction and the rotor is relatively light and thereforeadapted to be mounted directly upon the shaft or axle which it is todrive. The stator on the other hand maybe supported independently andeven have a limited independent motion, since such independent motionwill 'ferred to 1s have no harmful efiect on the rotor. Where largetorque is re uired, as many of the disc armatures may e mounted on theshaft as found necessary. Because of the open construction both rotorand stator may be designed for heavy currents and because of the simpleconstruction of the rotor, hi h 1 speed may be obtained-without danger,t e

induction motors and, therefore, will vary but a few percent whenrunning as a motor at full load and when running as an inductiongenerator.

What I claim is:

1. In a variable speed induction motor, a rotating armature,statorwindings movably supported at opposite sides of the armature axis forimposing a rotating etic field on the armature and means for simul-.

taneously shifting said stator windings toward and away irom each othersubstantially radially of the armature.

2. In a variable speed induction motor, a

rotating armature, stator windingsmovably- 7 supported at opposite sidesof the armature axis and interconnected to travel in opposite directionssubstantially radially of the armature and controlling means foreffecting such radial adjustment of the stator wind- 1n In a variablespeed induction motor, a rotating armature, stator windings movablysupported at opposite sides of the armature ax1s and interconnected totravel in oppo- "site directions substantially radially of the armatureand means for automatically effecting radial adjustment of the statorwindingsin accordance with operating conditions i of the motor. slip canbe made to approximate closely that obtained in the present commercialdesign of 4. In a variable speed polyphase induction motor, a rotor,stator elementsmovabl supported at opposite sides of the rotor axis andmeans for gradually shifting said stator elements toward and away fromeach other to thereby vary the angular s ed of the magnetic fieldimposed by said elements upon the rotor.- I

In witnesswhereo'f, I have hereunto set my hand this 24th day ofOctober, 1922.

Davn) G. HOWARD.

